Gate-last, High-k Metal Gate (HKMG), also called replacement gate or replacement metal gate, techniques have been developed to address problems attendant upon substituting metal gate electrodes for, for example, polysilicon gate electrodes. In such a process, the polysilicon gate electrodes, also referred to as sacrificial gate electrodes or dummy gate electrodes in such a process, are replaced with metal gate material. The sacrificial gate electrode holds the position for the subsequent metal gate electrode to be formed. For example, an amorphous silicon (a-Si) or polysilicon gate may be used during initial processing until a high-temperature annealing to activate source/drain implants has been completed. Subsequently, the a-Si or polysilicon may be removed and replaced with a metal gate.
Replacement gates are being employed, especially in 32 nm, 28 nm, and 22 nm technology nodes. However, as technology nodes continue to decrease, there are challenges in using replacement gate technology. In particular, conventional processing can result in variation in the height of the resultant replacement metal gates. Further, as the gate pitch scales down, the inter-layer dielectric (ILD) gap fill becomes challenging. Flowable dielectric material (e.g., flowable oxide) is able to resolve this gap fill issue. However, the quality of flowable dielectric is typically poor, and the flowable dielectric may be vulnerable to subsequent wet/dry etch processing (such as an HF pre-clean before high-k deposition). Significant dielectric loss can occur if subsequent wet/dry etch processing is excessive.
Accordingly, a need exists for enhanced processing and structures to facilitate gate height uniformity in a replacement gate process, while providing better protection of the inter-layer dielectric.